In cracking operations, such as the pyrolytic cracking of ethane, propane, and naphthas to form olefins, oxygenated compounds, including carbonyl compounds are formed, the amount of carbonyl compounds, such as aldehydes and ketones, formed in such operations can vary widely, but is typically about 1 to 100 parts per million in the gas stream with concentrations as high as 1000 parts per million, occasionally being encountered because of the utilization of various feedstocks and cracking temperatures.
When the gas stream is passed through a basic wash (pH&gt;7) to remove acidic components such as hydrogen sulfide and carbon dioxide, oxygen containing compounds, such as the carbonyl functionality compounds, particularly acetaldehyde, will undergo polymerization in the presence of the basic wash or scrubbing conditions. In the wash tower, the resulting polymer will settle on the trays leading to fouling and eventual plugging of the trays, which means the unit must be shutdown for cleaning which can be a costly operation. The basic wash systems, where treatment is required to inhibit such polymer-based fouling, include amine acid gas scrubber, such as MEA, DEA, isopropyl amine, butyl amine, etc. and caustic wash systems.
Generally, the basic washing entails contacting the gaseous olefins with an aqueous basic solution in a wash tower to remove hydrogen sulfide, carbon dioxide and other oxygenated compounds therefrom. The basic washing is particularly appropriate for the basic washing process which follows the pyrolytic cracking of such hydrocarbons as ethane, propane, butane, naphtha and mixtures thereof to produce the corresponding gaseous ethylene, propylene, butadiene and the like, containing the carbonyl and other contaminants.